If you use a pattern to build a clothing line, you are, in essence, making a "cover" of the design. Just like a singer may "cover" a song by Metallica. However, if the singer hasn't obtained permission to perform and sell copies of his cover, then he will end up in court and will have to pay a huge fine, Metallica's legal fees, and money owing to the band. If you wanted to build your clothing line, and wanted to avoid law suits, you would just go to the designer and negotiate a deal for use of the pattern.
It's pretty common for photos and artwork to be published with an acknowledgement of the photographer/artist either under the photograph, or in footnotes, or in a separate credit list.
In theatre/film/tv productions, everyone who worked on the project, or helped with the project, is named above or below the line as appropriate. Accountants, personal assistants, boom operators, drivers and so on are all listed. In some projects, say for a TV series, the person who had the original idea with be credited with the line "Concept by", the person who develops the idea into a script gets a writer's credit, the person who punches up the script gets credit for "additional material".
On a program, the artist who designed the cover, even though paid for this service, gets credited within the body of the program.
In the section dealing with costumes, functions are spelled out. The designer may have an assistant, the cutter and dyer and seamstress may also be credited, as is the wigmaster, and the wardrobe mistress. All work under costumes, all are credited, yet it is clear who had the concept for the original designs, who made some changes, who built the costumes, and who maintains the costumes.
A friend's husband is hired by inventors to build their prototypes, sometimes to scale, so they can test their ideas for weaknesses. He never gets credit for his crucial work in detecting flaws and hazards. But he gets very good money for his work in compensation.
DG did not have the original idea and, IIRC, the device didn't work. But perhaps DG could not separate himself from his work, and needed to retain ownership of his "improvements". DG may have have serious boundary issues and just seen AL as an extension of his own persona. I wonder if the "cheating" that got DG thrown out of univerity was plagairism.